Add Sansa Clip+ target to test mkamsboot

UNTESTED, could ver well brick your Clip+
If it works, booting should just be delayed by a small delay (perhaps
not noticeable)
Hopefully the Clipv2 checks will work for Clip+ and then we'll be able
to test the other Clipv2 code (LCD/button)

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@24219 a1c6a512-1295-4272-9138-f99709370657
9 files changed